New and more energy efficient illumination devices are being developed every day. They are often based on common technologies utilizing solid state light sources such as Light Emitting Diodes (LEDs). Most, if not all, commercially available solid state light sources having a high efficiency emit light of undesired wavelengths e.g. UV, blue, violet etc. Hence, there is often a wavelength converter present which converts light of a shorter wavelength, into light of a longer wavelength in a highly transparent luminescent material. The wavelength converter then produces light of a pleasing aesthetic wavelength similar to e.g. natural white light.
For a new kind of energy efficient lighting device to replace the current regime of incandescent light bulbs it would be beneficial if such a device would work as a retrofit of the incandescent bulb. A retrofit could for example have a similar outside form factor, which is commercially available today, where solid state light sources are mounted within some kind of bulb shaped cover structure, thus providing the look, i.e. aesthetic, of an incandescent bulb. However, just the aesthetic characteristic of an incandescent bulb may not entirely please all customers. The light distribution from a retrofit bulb should also be uniform. The currently available replacement light bulbs most often comprise solid state light sources which are arranged on a flat circuit board and placed in the bulb. Thus, the light distribution, i.e. luminance, of these bulbs is not as uniform as the light distribution from an ordinary incandescent bulb.
US patent application 2004/0008525 tries to remedy the problem of an uneven light distribution by introducing a LED lamp chain on which a plurality of light emitting diodes are arranged and which is placed in a bulb, and wherein fluorescent material may be included in the bulb material. However, the solution may not provide a uniform light distribution of desirable wavelengths, and the fluorescent material may experience an uneven luminance and the light from the bulb may be perceived as spotty.
US2004/0007980A1 discloses a LED chain body formed by connecting a plurality of LED via flexible members and which is inserted into a transparent or translucent tube. WO2012/085736A1 discloses a light guide in the form of a continuous optical element in which a string of a plurality of LEDs is arranged and in which the LEDs may be mounted on a small flexible PCB with the continuous optical element on top of it or encapsulating it.
Hence, there is a need for a lighting device which replaces the incandescent bulb, advantageously such a lighting device is a retrofit of the current design and thus able to fit into current lighting fixtures in use today. Further, such a device is desirably simple, cheap, and configured such that current mass-manufacturing techniques are easily applied to manufacture it.